The present invention generally relates to the field of information storage, and more particularly to a circuit and method for detecting faults on a write head of a hard-disk drive.
Hard-disk drives are mass storage devices that may include a magnetic storage media, e.g., rotating disk or platters, a spindle motor, read/write heads, an actuator, a preamplifier, a read channel, a write channel, a servo circuit and control circuitry to control the operation of the hard-disk drive and to properly interface the hard-disk drive to a host system or bus. FIG. 1 shows an example of a prior art disk drive mass storage system 10. Disk drive system 10 includes a number of rotating platters 12 mounted on a base. Platters 12 are used to store data that is represented as magnetic transitions on the magnetic platters 12, with each platter 12 coupleable to an arm 14 having a read head 16 and a write head 18 at the tip thereof. The read head 16 and write head 18 are adapted to transfer data to and from the platters 12 via a preamplifier 20. The preamplifier 20 is coupled to circuitry 22 that processes the data being read from and written to platters 12 and controls the various operations of disk drive system 10.
Data is stored to and retrieved from each side of magnetic platters by write heads 18 and read heads 16, respectively, at the tip of arms 14. The read heads 16 comprise magneto-resistive heads adapted to read data from platters 12 when current is passed through them. The write heads 18 comprise inductive wires (coils) that transmit data to magnetic media platters 12. Heads 16, 18 are coupled to preamplifier 20 that serves as an interface between read/write heads 16/18 of disk drive system 10 and circuitry 22. The preamp 20 may comprise a single chip containing a reader amplifier, a writer circuit, fault detection circuitry, and a serial port interface, for example.
The write head 18 comprises a coil through which current is passed to create a magnetic field and write data onto platters 12. A problem in hard-disk drive systems 10 is that the write head 18 coil may be open or short at various times during manufacturing or in the field for a variety of reasons. The open or short faults may occur due to a faulty coil that has severed, creating an open circuit, or a faulty coil that has fused together, creating a short circuit. If the hard-disk drive is moved, the vibration may cause the write head coil to temporarily short to ground, for example. In any of these situations, the write head fault needs to be reported immediately, for example, from preamplifier 20 to circuitry 22. If the write head 18 coil is permanently damaged, it needs to be repaired or replaced. Furthermore, the electrical resistance of the write head 18 coil may be too high to function properly.
Because these faults in the write head 18 coil can occur, a hard-disk drive system 10 requires a function to detect write head 18 faults. Prior art write fault detection methods typically are performed during the write mode, a very noisy mode. Typically, a hard-disk drive system 10 has two active operating modes: a read mode during which data is read from platters 12 via read heads 16, and a write mode, during which write heads 18 write data to platters 12. The reamplifier 20 includes control circuitry for both the read head 16 and the write head 18. Therefore, it has two exclusive active operation modes: read and write. The read mode is a more passive, quiet and steady mode, and the write mode is more of an active mode, because a large amount of current (usually around 30 to 70 mA), with the current polarity being switched frequently, for example, every 1 or 2 nanoseconds, is passed through the coil in order to write data to platters 12.
During the write mode, the preamplifier 20 provides a substantial current to write head 18 coil to create a magnetic field that writes data to the platters 12. More recent designs of hard-disk drive systems 10 have higher data rates such as 1 gigabits per second, and the write current has to switch direction or polarity faster, accordingly. This results in a complicated write signal waveform, making it difficult to detect write head faults correctly. For example, when the write head is operating normally at high data rate, prior art methods of detecting write head faults may give a false detection and indicate that the write head has an open fault or short to ground. Alternatively, write head faults may not be detected with prior art detection circuits and methods due to their limited frequency range for correct operation.
The present invention provides an accurate circuit and method for detecting write head faults in a disk drive circuit. The fault detection is performed during a read mode using a small DC current, avoiding problems that arise when performing a write head fault detection during the write mode of a hard-disk drive. Several devices that may be pre-existing in a writer circuit are used to build the present DC detection circuit, which provides reliable and accurate write fault detection while minimizing the circuit overhead needed to perform the write head fault detection function. A first and second serially connected resistor having equal values are coupled across the coil of the write head, with a transistor coupled to a common node between the two resistors and ground to maintain a DC current path to ground. The voltages across the two resistors and with respect to the common node are analyzed to determine the fault status of the write head coil.
Disclosed is a circuit for detecting faults on a write head of a hard-disk drive. The circuit includes a first resistor coupled to a first end of the write head coil at a node a, and a second resistor coupled to a second end of the coil at a node b. A transistor is coupled to the first and second resistors at a common node c. Faults on the write head coil are detectable by analyzing the voltages across the nodes a, b and c.
Also disclosed is a method of detecting faults on a write head of a hard-disk drive. The method comprises the steps of coupling a first end of the write head coil to a first resistor at a node a, coupling a second end of the coil to a second resistor at a node b, and coupling a transistor to the first and second resistors at a common node c. Faults are detected on the coil by analyzing the voltages across nodes a, b and c.
The present invention provides a reliable, accurate means of detecting faults on a write head of a disk drive system by performing a write head fault detection during a quiet operating mode of the hard-disk drive. Errors in write head fault detection are avoided by use of the present invention. Standard components are utilized that are inexpensive and easily implementable into electronic circuitry. The invention is advantageous in discriminating between an open or short fault, which is not possible with prior art fault detection circuits. The write head fault detection is frequency-independent because the detection is performed during a non-writing mode. Transient faults with short duration ( less than 150 nanoseconds) are ignored by means of a timing delay.